Using a novel methodological approach, scientists of the Potsdam Institute for Climate Impact Research (PIK) have introduced new estimates on how climate change will affect water availability.

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Access to freshwater in Africa and the Middle East is known to be scarce, but the Siberian tundra and Indian grasslands also lack freshwater. These areas along with dry pockets across the globe are expected to expand and create implications for their habitats and communities.

The new study predicts that if global warming is limited to 2 degrees above pre-industrial levels, 500 million people could be subject to increased water scarcity. And at 5 degrees global warming almost all ice-free land might be affected by ecosystem change.

"We managed to quantify a number of crucial impacts of climate change on the global land area," says Dieter Gerten, lead-author of one of the studies. Mean global warming of 2 degrees, the target set by the international community, is projected to expose an additional 8 percent of humankind to new or increased water scarcity. 3.5 degrees — likely to occur if national emissions reductions remain at currently pledged levels — would affect 11 percent of the world population. 5 degrees could raise this even further to 13 percent.

"If population growth continues, by the end of our century under a business-as-usual scenario these figures would equate to well over one billion lives touched," Gerten points out. "And this is on top of the more than one billion people already living in water-scarce regions today." Parts of Asia and North Africa, the Mediterranean and the Middle East are particularly vulnerable.

"The area at risk of ecosystem transformation is expected to double between global warming of about 3 and 4 degrees," says Lila Warszawski, lead author of another study that systematically compared different impact models — and the associated uncertainties — in order to gain a fuller picture of the possible consequences of climate change for natural ecosystems. This is part of the international Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP).

A warming of 5 degrees, likely to happen in the next century if climate change goes on unabated, would put nearly all terrestrial natural ecosystems at risk of severe change. "So despite the uncertainties, the findings clearly demonstrate that there is a large difference in the risk of global ecosystem change under a scenario of no climate change mitigation compared to one of ambitious mitigation," says Sebastian Ostberg, lead author of the third study.